Modeling the Impact of Modified Inertia Coefficient (H) due to ESS in Power System Frequency Response Analysis

Abstract

The advantages of increased penetration of distributed generation are also accompanied by several challenges, low inertia being one of them, which threatens the grid stability. An emerging approach to confront this problem is the introduction of so-called virtual inertia (VI) provided by energy storage systems (ESS). In contrast to the already available literature which considers a conventional load frequency control (LFC) model, this work concentrates on a modified LFC model as the integration of a large portion of ESS changes the inertia constant (H) of a power system. A sensitivity function is derived that shows the effects of changes in H on the power system's frequency response. With the help of the developed mathematical model and simulation results, it is shown that a difference in the actual and calculated values of H can deteriorate the system performance and economy. As one of the reasons for this difference is improper modeling of ESS in the LFC model, therefore, the study signifies the accurate calculation of H in the power systems having enlarged penetration of ESS.

Mitigation of Over-Frequency through Optimal Allocation of BESS in a Low-Inertia Power System

“…Let us assume that transmission line impedance Z is written by Equation (5). Thus, expressions of real and reactive power can be further expanded and written via Equations ( 6) and (7).…”

“…where R and X refer to the transmission line resistance (in p.u) and reactance (in p.u), respectively. Thus, Q-V curve can be achieved by solving Equations ( 6) and (7). However, near the lowest point (i.e., the voltage collapse point) of the Q-V curve, the Jacobian matrix becomes singular and, consequently, obtaining numerical solution becomes difficult.…”

“…These WTGs are interfaced with the grid via power electronic converters, which decouple them from the corresponding network [6]. Consequently, these machines usually do not offer inertia and governor response to control system frequency [7]. Therefore, under high wind penetration, maintaining an adequate frequency response is becoming challenging due to the presence of a few synchronous generators in a low-inertia grid.…”